In the case of voltage converters for high alternate input voltages or direct voltage as known from prior art, a peak value of the rectified voltage is impressed on a high-capacity capacitor located directly at the outputs of a rectifier. Consequently, very expensive charge circuits with pre-charging capability had to be implemented, for example, by including a resistor and subsequent bridging with ground contacts.
Also, so-called "double-booster" topologies have been known; these comprise an intermediate circuit including with an electrolyte capacitor in such a manner that the latter or the upstream mains is subjected to a load when the high input voltage is impressed due to the feedthrough, without short circuit limit. Therefore, this capacitor must be configured for the peak voltage at the input, whereby this peak voltage is greater than the booster's regulated output voltage.
Furthermore, in controlling high input voltages and currents, problems occur concerning the components used. The semiconductors such as transistors and diodes used must be adapted to the maximum input voltage or current, and the transformers used must be adapted from the viewpoints of power, as well as voltage, to the input voltage to be processed, whereby unacceptable winding and coil voltages occur.
In the case of known converters, which use power transistors as switching elements, the permissible input voltage is limited by the load capability of the type of power transistor used. When several synchronously clocked transistors are connected in series and/or parallel, the problem of voltage and/or current balancing arises, one example of this being the connection of loss-prone RCD line branches parallel to the transistor break distance.
DE 4,414,677 A1 has suggested a primary switched voltage converter with a primary side composed of several serially connected partial systems, each including a transistor circuit breaker arrangement, whereby each of these systems is associated with a separate transformer primary winding, which, in turn, are coupled into a common load output over the secondary side of the converter. Due to the transformer winding voltage, this coupling effects automatic, dynamic and quasi loss-free voltage balancing between the partial systems under load.
In the case of this form of embodiment the transformer windings are connected "hard" parallel on the secondary side. This has the disadvantage that the absence of balances results in dynamic circulating currents--which are not current-limiting--but effect balancing.
Also this circuit layout has the disadvantage that, in the case of converters with alternating current input, a peak value of the rectified voltage is impressed directly on a high-capacity capacitor located directly at the output of a rectifier and that all of these flow-through converter topologies do not permit a power take-up (Power Factor Correction=PFC) adapted to the waveform of the input voltage.
Therefore, the problem to be solved by the invention herein provides a converter for high input voltages or input currents, said converter having a simple design and improving voltage or current balancing.